This application claims the benefit of Korean Application No. 2000-72123, filed Nov. 30, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing a micromirror actuator, and more particularly, to a method of manufacturing a micromirror actuator that increases a flatness of a micromirror through the lamination of a film-type organic layer and a simplified process of planarizing the micromirror.
2. Description of the Related Art
A micro optical cross connector (MOXC) as used in optical communications is a device that selects an optical path to allow an optical signal to be transmitted from a certain input terminal to a certain output terminal. The core element of the MOXC in optical communications is a micromirror. Thus, the optical communication efficiency and performance of the MOXC is strongly dependent on the reflectivity of the micromirror and the ability of the micromirror to stand erect.
Referring to FIG. 1, a conventional micromirror actuator includes a substrate 100, a trench 105 formed in the substrate 100, lower and side electrodes 110 and 113 formed at a corresponding bottom and side of the trench 105, posts 115 that protrude from the substrate 100 in an area outside the trench 105, torsion springs 120 supported by the posts 115, and a micromirror 125 elastically supported by the torsion springs 120 to be capable of rotating.
The micromirror 125 can be rotated by electrostatic forces generated through an interaction with the lower electrode 110. The micromirror 125 can stand erect due to an interaction with the side electrode 113. The micromirror 125 can also maintain its parallel state when voltage is turned off. A micromirror actuator having the above structure can select an optical path by reflecting optical signals when the micromirror 125 stands erect over the substrate 100, and also allows the optical signals to directly pass over the surface of the micromirror 125 when the micromirror 125 is parallel with the surface of the substrate 100.
When the micromirror actuator has the trench 105, it is necessary therefore to planarize the micromirror 125 to increase its reflectivity. FIGS. 2A through 2C are cross-sectional views illustrating a conventional method of manufacturing the micromirror actuator as viewed along line Vxe2x80x94V of FIG. 1. The conventional process of planarizing the micromirror actuator includes forming the trench 105 by etching a portion of a silicon wafer 130 to a predetermined depth (shown in FIG. 2A), thickly depositing a photoresist 135 by spin coating (shown in FIG. 2B), and planarizing the photoresist 135 by chemical mechanical polishing (CMP) (shown in FIG. 2C).
However, when the photoresist 135 is planarized by CMP, a cushion phenomenon occurs causing the surface of the photoresist 135 to become irregular as shown in FIG. 3. In other words, the planarization of the photoresist 135 is performed while applying weight to the photoresist 135 in a lapping device (not shown). However, when the silicon wafer 130 is taken out from the lapping device after completing the planarization of the photoresist 135, the cushion phenomenon occurs at the photoresist 135. The cushion phenomenon occurs when a predetermined portion of the silicon wafer 130 to which weight has been applied swells up. The reason the cushion phenomenon occurs will be described in the following.
In FIG. 2B, the photoresist 135 deposited to a predetermined thickness h on the silicon wafer 130 is soft. In addition, the height of the photoresist 135 deposited over the trench 105 is less than the height of the photoresist 135 deposited outside the trench 105 by as much as a height difference of hxe2x80x2. Accordingly, the photoresist 135 deposited over the trench 105 is slightly recessed when the photoresist 135 is polished by CMP to planarize its surface.
After polishing of the photoresist 135, the hardness of the resulting structure in a trench region becomes different from the hardness of the resulting structure outside the trench region. In other words, the lengthwise hardness of the structure including the photoresist 135 and the silicon wafer 130 in the trench region is equal to the sum of the hardness of photoresist 135t1 remaining over the trench 105 after the CMP, the hardness of photoresist 135t2 filling the trench 105, and the hardness of a lower wafer 130t under the photoresist 135t2. On the other hand, the lengthwise hardness of the structure outside the trench region is equal to the sum of the hardness of photoresist 135n remaining on the silicon wafer 130 outside the trench 105 after the CMP and the hardness of a lower silicon wafer 130n under the photoresist 135n. Here, since the hardness of the silicon wafer 130 is greater than the hardness of the photoresist 135, the lengthwise hardness of the structure including the photoresist 135 and the silicon wafer 130 is greater outside the trench region than in the trench region. Accordingly, the photoresist 135 expands more in the region of the trench 105 than in the region around the trench 105, producing a swell C on the surface of the photoresist 135 as shown in FIG. 3. This swelling effect is referred to as the cushion phenomenon.
As described above, if the CMP that is usually applied to silicon is directly performed on the photoresist 135 deposited over the trench 105, the photoresist 135 cannot be planarized because of the cushion phenomenon. In order to properly planarize the photoresist 135, the CMP must therefore be performed twice. Accordingly, the costs of the planarization increases, the reflectivity of the micromirror may deteriorate, and an optical loss may increase.
To solve the above and other problems, it is an object of the present invention to provide a method of manufacturing a micromirror actuator that increases a flatness of a micromirror by laminating a film-type polyimide layer, enhances a reflectivity of the micromirror, and simplifies a process of planarizing the micromirror.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, a method of manufacturing a micromirror actuator according to an embodiment of the invention includes forming a trench on a substrate by etching, laminating a film-type organic layer on the substrate to cover but not fill the trench so that the trench remains hollow, depositing and patterning a metal layer on the film-type organic layer, and removing the film-type organic layer.
According to another embodiment of the invention, the method further includes forming a lower electrode and a side electrode by depositing and patterning an insulating layer and a metal layer on the substrate after forming the trench region, forming post holes by patterning the film-type organic layer after laminating the film-type organic layer, and forming a micromirror, torsion springs, and posts by patterning the metal layer on the film-type organic layer, and removing the film-type organic layer.